Our studies demonstrate marked immune depression, i.e., decreased T cell and macrophage (MO) antigen presentation function and increased lethality from subsequent sepsis, in young males;but not in proestrus females following trauma-hemorrhage (T-H). The results also demonstrate a compartmentalized response in males;splenic and peritoneal MO (SMO, PMO) cytokine release is decreased, while Kupffer cells (KC) and alveolar MO cytokine release is markedly increased. Thus, it is important to identify agents that have global immunomodulating effects under those conditions. Our findings that 17p-estradiol (E2) has the unique ability to protect immune cell responses following T-H, and that flutamide [androgen receptor (AR) antagonist] also utilizes E2-mediated pathway in restoring immune functions in males, leads us to hypothesize that female sex steroids play a critical role in maintaining cell signaling homeostasis and the immune cell functions in various tissue compartments after T-H. Since activation of MO/T cell precedes a cascade of signaling events, we will characterize signaling alterations in Kupffer cells, alveolar MO, PMO, SMO, splenic dendritic cells (DC) and splenic T cells, peripheral blood monocytes and T cells and correlate those changes with their effector responses (MO and DC: MO/DC antigen presentation and ability to release cytokines;T cells: ability to differentiate into Th1/Th2 phenotype following T-H in males/proestrus females). Estrogen receptor (ER) and AR expression will also be evaluated. Studies will also examine if modulating alterations in one or more signaling pathways, identified in the above studies, by treating mice with E2 or flutamide following T-H normalizes MO, DC and T cell effector responses. Furthermore, we will use E2 (cell permeable) and E2 conjugated with BSA (bovine serum albumin;cell impermeable) to determine the contribution of nuclear vs. surface receptor in restoring immune cell responses after T-H. Additional studies will examine whether E2 and flutamide utilize a common or different signaling pathway in mediating their salutary effects after T-H. Moreover, ER-a and ER-(3 knockout (KO) mice will be used to determine the relative role of ER-a and ER-p in normalizing immune cell responses after T-H. Studies will also utilize other available KOs and pharmacological agents to delineate which of the signaling pathway(s) is/are critical to E2-mediated salutary effects in various tissue compartments following T-H. Finally, we will determine whether the agent(s) that normalizes immune cell responses has/have any salutary effects in decreasing the mortality rates from sepsis following T-H. The proposed studies using state-of-the-art cellular/molecular techniques should provide innovative information identifying the mechanism(s) by which sex steroids maintain or deteriorate immune cell functions in various tissue compartments following T-H, and also for developing gender specific therapy for preventing immune depression and reducing mortality from sepsis in trauma victims.